PALEOCLIMATIC INTERPRETATION OF THE WOOD STRUCTURES OF THE TREES IN THE CHINLE FORMATION (UPPER TRIASSIC), PETRIFIED FOREST NATIONAL-PARK, ARIZONA, USA

Typically, the fossil woods in the Upper Triassic Chinle Formation in Petrified Forest National Park, Arizona, USA do not show annual growth rings but contain irregular growth interruptions similar to those found in trees now growing in the humid tropics. These interruptions could be due to endogenous hormonal effects or to occasional local variations in water supply. Therefore, it is concluded that the Late Triassic fossil forests in the park lived in conditions that permitted continuous tree growth. Limited data from areas outside of the park suggests that similar conditions prevailed in adjacent areas in the southwestern United States during the Late Triassic. Although this region is reported to have been under the influence of a monsoonal circulation pattern during the Late Triassic, the growth of the trees does not appear to have been greatly affected.